"You shouldn't walk in heels higher than three inches," she said. "Anything over the three-inch mark changes the biomechanics of how you walk—your strides are shortened, you can't walk as fast, your body weight shifts to the ball of the foot, which throws off your center of gravity and stresses the knees and lower back." Well there you have it. Head over to InStyle to learn more from Dr. Splichal.